Certain proposed mass transfer tray constructions are equipped with contact and separation elements (CSE) featuring a firmly attached axial swirler at the inlet end and a cyclone separator at the outlet end (Inventor's Certificate USSR, No. 345926, Class B01D 3/20). The supply of the liquid into the contact zone is realized by two rows of annular holes. One is located in the area of the inclined vanes of the axial swirler, and the other is below the swirler. The disadvantage of this type of tray lies in the low level of effectiveness of mass transfer due to undesirable (parasitic) flows in two directions. The first undesirable flow occurs in the free space between the column shell and the CSE, with some part of the liquid flowing from the tray plate directly to the weir without having mass transfer contact with the gas phase. The second undesired flow concerns the backflow of liquid that has already finished the mass transfer process and is now flowing back from the separator to the annular holes, which are intended for supplying liquid for contact with the gas entering the CSE.
Furthermore, a swirler contact element is known (CSE) (inventor's certificate USSR No. 475160, Class B01D 3/30), containing a nozzle with a row of annular holes at its input end and a hollow cyclone separator at its output end. An axial swirler is firmly attached in the perforation zone and contains several inclined vanes. The nozzle features an annular rib at its outer side between the swirler and the separator.
Contrary to the CSE described above, this type of construction allows for a significant increase of the technical-economic performance parameters of the tray. The known CSEs, however, limit the intensity of the mass transfer and, thus, also the effectiveness of the tray.
Another highly effective swirler contact element is known (CSE) (U.S. Pat. No. 4,838,906, U.S. Class 55/238 and European Patent No. 0281628 B1). It contains a short nozzle with a row of annular holes at its input end and a complex axial swirler inside. The firmly attached axial swirler of this CSE has inclined vanes in the upper section and a dense net of short vertical vanes arranged lengthwise to the nozzle axis in the lower section, with the number of straight vanes being at least twice the number of inclined vanes. This cyclone separator may be operated in one or two stages.
Such a construction allows a significant increase of the effectiveness of the mass exchange and the separation of the phases within one single element. However, the mere arrangement of a series of CSEs on a tray does not guarantee the desired high level of mass transfer intensity. Due to the undesired (parasitic) flows on the tray past the CSEs and to the backflow from the separator exit via one deflection ring along the outer wall of the CSE to the annular holes to be once more in contact with the gas, the actual new liquid flow leaves the tray without establishing contact.
Experience collected during practical applications of the CSE in industry shows that not only is an optimal choice of the CSE dimensions and shape a necessity, but also required is an improved organization of the flow of liquids on a tray equipped with CSEs. Here it should be noted that no intensive mixing of the fluid through the gas bubbles occurs on CSE trays, which stands in contrast to bubble cap trays where an intensive thorough mixing of the liquids is performed while they flow from one side of the tray to the other.